Vehicle seat structure

Abstract

A seat back ( 20 ) includes an upper thoracic support section ( 20 a ) for supporting at least a portion corresponding to a lower part of the upper thoracic spine of a seated occupant, and a lower thoracic support section ( 20 b ) disposed on a front side with respect to the upper thoracic support section ( 20 a ) and configured to support a portion corresponding to the lower thoracic spine of the seated occupant. The lower thoracic support section ( 20 b ) is configured to displace backward greatly, as compared with the upper thoracic support section ( 20 a ) in such, a way that the upper thoracic spine of the seated occupant is inclined forward, when backward inertia force acts on the seated occupant.

The invention claimed is:  
     
       1. A vehicle seat structure provided with a seat cushion and a seat back, wherein
 the seat back includes:
 an upper thoracic support section for supporting at least a portion corresponding to a lower part of the upper thoracic spine of a seated occupant; 
 a lower thoracic support section disposed on a front side with respect to the upper thoracic support section and configured to support a portion corresponding to the lower thoracic spine of the seated occupant; 
 a lumbar support section disposed on the front side with respect to the lower thoracic support section and configured to support a portion corresponding to the lumbar spine of the seated occupant; 
 an upper middle support section disposed between the upper thoracic support section and the lower thoracic support section; and 
 a lower middle support section disposed between the lower thoracic support section and the lumbar support section; and 
 
 wherein 
 a spring constant of the lower thoracic support section is lower than a spring constant of the upper thoracic support section and a spring constant of the lumbar support section, 
 a spring constant of the upper middle support section is set to an intermediate value between a spring constant of the upper thoracic support section and a spring constant of the lower thoracic support section, and 
 a spring constant of the lower middle support section is set to an intermediate value between a spring constant of the lower thoracic support section and a spring constant of the lumbar support section. 
 
     
     
       2. The vehicle seat structure according to  claim 1 , wherein
 the upper thoracic support section includes a part having a spring constant substantially equal to a spring constant of the lumbar support section. 
 
     
     
       3. The vehicle seat structure according to  claim 2 , wherein
 the upper thoracic support section includes a part having a spring constant larger than a spring constant of the lower thoracic support section by 20 N/m or more. 
 
     
     
       4. The vehicle seat structure according to  claim 1 , wherein
 the upper thoracic support section includes a part having a spring constant in a range from 5/4 to 7/4 of a spring constant of the lower thoracic support section.